The use of radioiodine to label organic compounds for use in diagnostic nuclear medicine is known. For example, Blan et al., in Int. J. App. Radiat. Isoropes, 3, pp. 217-225 (1958), described the use of p-iodobenzoyl chloride (I-131) to label antibiotics for the determination of in vivo protein distribution. Bolton and Hunter, Biochem. J., 133, pp. 529-539 (1973), reported that the N-hydroxysuccinimide ester of 3-(4-hydroxyphenyl)-propionic acid-.sup.125 I is useful to radio-label proteins. Smith, in U.S. Pat. No. 3,979,506, described imido esters of radionuclide-substituted hydroxy or alkoxy phenyls wherein the nuclide can be I-125. Wieland et al., in J. Nucl. Med., 22, 358-364 (1981) described the use of [.sup.123 I] and [.sup.131 I] metaiodobenzylguanidine to image primate adrenal medulla. Kline et al. reported on the myocardial imaging in man with [.sup.123 I] meta-iodobenzylguanidine; J. Nucl. Med., 22, 129-132 (1981).
An excellent review of the theory and practice of nuclear medicine is found in "Nuclear Cardiology For Clinicians" edited by Soin and Brooks, Futura Publishing Company, Mount Kisco, N.Y., 1980. A survey of radiopharmaceuticals and their use in nuclear medicine was written by Cornsell and Ice in "Drug Design", Vol VI, E. J. Ariens, Ed., Academic Press, New York, N.Y. 1975, Chapter 4.
Molloy et al., in U.S. Pat. No. 4,289,787, disclose a new group of quaternary ammonium compounds that are useful in treating cardiac arrhythmias and prolonging the action potential duration of cardiac tissue. Of particular interest with the group is the compound N,N-diethyl-N-n-heptyl-4-(4-chlorophenyl)butylammonium phosphate, now generically referred to as clofilium.
It has now been found that clofilium, and compounds similar in structure to clofilium, are particularly effective in binding to certain animal tissue, especially cardiac tissue. Accordingly, it is an object of this invention to provide certain quaternary ammonium compounds bearing a radioiodine atom as a label. Such compounds are useful as imaging agents, particularly cardiac imaging agents.